This invention relates to the field of pelletizers for food processors. In particular, this invention relates to the mounting of dies in a food pelletizer.
Pelletizers are well-known in the field of food and feed processing. A conventional pelletizer comprises a two part die housing supporting a cylindrical shaped annular die. The die has a radially inner face and radially outer face with slots between the two faces. The die housing supports the edges of the die. The die housing is rotatably mounted to a frame. The die and die housings together define an interior pelletizing chamber. Located within the pelletizing chamber are a series of rollers supported by a roller frame. The roller frame is fixed and rotatably supports the rollers in intimate contact with the radially inner surface of the die. The die housing is driven by a motor or other mechanism to produce rotation of the annular die. The rollers, not being directly driven, are in contact with the radially inner surface of the die and are caused to rotate by the motion of the die.
Conditioned feed material is introduced into the pelletizing chamber. The feed is then captured between the rollers and the radially inner surface of the die. The rollers next extrude the feed through the slots in the die. Knives or cutters are located around the radially outer surface of the die to shear the extruded feed material from the radially outer surface of the die to form pellets.
In a conventional pelletizer, the die housing contacts the edges of the annular die and extends in a manner to form a lip in close contact with at least a portion of the outer circumferential surface of the die. In some designs, the die and die housing are in direct contact along the die edges and portions of the radially outer surface of the die. Direct contact results in wear on both components. Wear of the components is reduced by hardening either or both of the die and die housing. As the components wear, they are re-machined for proper fit. Each re-machining decreases the operational life of the component. Additionally, the machining must be to high standards to preserve component alignment and therefore rotational balance.
In other prior designs, located between the outer circumferential surface of the die and the extended lip of the die housing is a die mount. The edge of the die continues to directly contact the die housing. The die mount or wear ring is employed between the die and die housing to extend the operational life of a particular die. Vibration and flexing of the die and die housing during operation of the pelletizer results in wear of the die mount. The die mount is intended to take up the wear that would normally be experienced by the die and therefore extend the operating life of the die. Die mounts are of a lower cost than dies, and therefore decrease the operating expense of a pelletizer.
A conventional die mount is of cylindrical construction with a rectangular cross section. The longer axis of the cross sectional rectangle is parallel to an axis of rotation defined by the die mount, die and die housing. While employment of the die mount is superior to direct die to die housing contact on the radially outer surface of the die, several disadvantages do exist from the present design. To preserve rotational balance, the die, die housing and wear ring must be manufactured to relatively high tolerances so as to preserve rotational balance. The cylindrical die mount requires periodic remachining to maintain high tolerances and therefore proper balance. Even slight variations in manufacturing tolerances can result in misalignment of the components and the inability to secure the components together for operation of the pelletizer. Even during set up of correctly machined components, the large sizes of the die and die holder can easily result in misalignment during assembly of the components. Misalignment of the components produces destructive imbalances during operation of the pelletizer.